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Neural Network on Microcontroller (NNoM)

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NNoM is a high-level inference Neural Network library specifically for microcontrollers.

[English Manual] [中文简介]


  • Deploy Keras model to NNoM model with one line of code.
  • Support complex structures; Inception, ResNet, DenseNet, Octave Convolution...
  • User-friendly interfaces.
  • High-performance backend selections.
  • Onboard (MCU) evaluation tools; Runtime analysis, Top-k, Confusion matrix...

The structure of NNoM is shown below:

More detail avaialble in Development Guide

Discussions welcome using issues. Pull request welcome. QQ/TIM group: 763089399.

Latest Updates - v0.4.x

Recurrent Layers (RNN) (0.4.1)

Recurrent layers (Simple RNN, GRU, LSTM) are implemented in version 0.4.1. Support statful and return_sequence options.

New Structured Interface (0.4.0)

NNoM has provided a new layer interface called Structured Interface, all marked with _s suffix. which aims to use one C-structure to provided all the configuration for a layer. Different from the Layer API which is human friendly, this structured API are more machine friendly.

Per-Channel Quantisation (0.4.0)

The new structred API supports per-channel quantisation (per-axis) and dilations for Convolutional layers.

New Scripts (0.4.0)

From 0.4.0, NNoM will switch to structured interface as default to generate the model header weights.h. The scripts corresponding to structured interfaces are while the Layer Interface corresponding to


NNoM is released under Apache License 2.0 since nnom-V0.2.0. License and copyright information can be found within the code.

Why NNoM?

The aims of NNoM is to provide a light-weight, user-friendly and flexible interface for fast deploying on MCU.

Nowadays, neural networks are wider, deeper, and denser.

[1] Szegedy, C., Liu, W., Jia, Y., Sermanet, P., Reed, S., Anguelov, D., ... & Rabinovich, A. (2015). Going deeper with convolutions. In Proceedings of the IEEE conference on computer vision and pattern recognition (pp. 1-9).

[2] He, K., Zhang, X., Ren, S., & Sun, J. (2016). Deep residual learning for image recognition. In Proceedings of the IEEE conference on computer vision and pattern recognition (pp. 770-778).

[3] Huang, G., Liu, Z., Van Der Maaten, L., & Weinberger, K. Q. (2017). Densely connected convolutional networks. In Proceedings of the IEEE conference on computer vision and pattern recognition (pp. 4700-4708).

After 2014, the development of Neural Networks are more focus on structure optimising to improve efficiency and performance, which is more important to the small footprint platforms such as MCUs. However, the available NN libs for MCU are too low-level which make it sooooo difficult to use with these complex strucures.

Therefore, we build NNoM to help embedded developers for faster and simpler deploying NN model directly to MCU.

NNoM will manage the strucutre, memory and everything else for the developer. All you need to do is feeding your new measurements and getting the results.

NNoM is now working closely with Keras (You can easily learn Keras in 30 seconds!). There is no need to learn TensorFlow/Lite or other libs.



5 min to NNoM Guide

The temporary guide

Porting and optimising Guide

RT-Thread Guide(Chinese)

RT-Thread-MNIST example (Chinese)


Documented examples

Please check examples and choose one to start with.

Available Operations

[API Manual]

*Notes: NNoM now supports both HWC and CHW formats. Some operation might not support both format currently. Please check the tables for the current status. *

Core Layers

Layers Struct API Layer API Comments
Convolution conv2d_s() Conv2D() Support 1/2D, support dilations (New!)
ConvTransposed (New!) conv2d_trans_s() Conv2DTrans() Under Dev.
Depthwise Conv dwconv2d_s() DW_Conv2D() Support 1/2D
Fully-connected dense_s() Dense()
Lambda lambda_s() Lambda() single input / single output anonymous operation
Batch Normalization N/A N/A This layer is merged to the last Conv by the script
Flatten flatten_s() Flatten()
SoftMax softmax_s() SoftMax() Softmax only has layer API
Activation N/A Activation() A layer instance for activation
Input/Output input_s()/output_s() Input()/Output()
Up Sampling upsample_s() UpSample()
Zero Padding zeropadding_s() ZeroPadding()
Cropping cropping_s() Cropping()

RNN Layers

Layers Status Struct API Comments
Recurrent NN Layer(New!) Alpha rnn_s() Layer wrapper of RNN
Simple Cell (New!) Alpha simple_cell_s()
GRU Cell (New!) Alpha gru_cell_s() Gated Recurrent Network
LSTM Cell (New!) Alpha lstm_s() Long Short-Term Memory


Activation can be used by itself as layer, or can be attached to the previous layer as "actail" to reduce memory cost.

There is no structred API for activation currently, since activation are not usually used as a layer.

Actrivation Struct API Layer API Activation API Comments
ReLU N/A ReLU() act_relu()
Leaky ReLU (New!) N/A LeakyReLU() act_leaky_relu()
Adv ReLU(New!) N/A N/A act_adv_relu() advance ReLU, Slope, max, threshold
TanH N/A TanH() act_tanh()
Hard TanH (New!) N/A TanH() backend only
Sigmoid N/A Sigmoid() act_sigmoid()
Hard Sigmoid (New!) N/A N/A N/A backend only

Pooling Layers

Pooling Struct API Layer API Comments
Max Pooling maxpool_s() MaxPool()
Average Pooling avgpool_s() AvgPool()
Sum Pooling sumpool_s() SumPool()
Global Max Pooling global_maxpool_s() GlobalMaxPool()
Global Average Pooling global_avgpool_s() GlobalAvgPool()
Global Sum Pooling global_sumpool_s() GlobalSumPool() dynamic output shift

Matrix Operations Layers

Matrix Struct API Layer API Comments
Concatenate concat_s() Concat() Concatenate through any axis
Multiple mult_s() Mult()
Addition add_s() Add()
Substraction sub_s() Sub()


NNoM now use the local pure C backend implementation by default. Thus, there is no special dependency needed.

However, You will need to enable libc for dynamic memory allocation malloc(), free(), and memset(). Or you can port to the equivalent memory method in your system.


CMSIS-NN/DSP is an optimized backend for ARM-Cortex-M4/7/33/35P. You can select it for up to 5x performance compared to the default C backend. NNoM will use the equivalent method in CMSIS-NN if the condition met.

Please check Porting and optimising Guide for detail.

Known Issues

The Converter do not support implicitly defined activations

The script currently does not support implicit act:

x = Dense(32, activation="relu")(x)

Use the explicit activation instead.

x = Dense(32)(x)
x = Relu()(x)


Jianjia Ma [email protected]

Also find me for field supports.

Citation are required in publication

Please contact me using above details if you have any problem.


  author       = {Jianjia Ma},
  title        = {{A higher-level Neural Network library on Microcontrollers (NNoM)}},
  month        = oct,
  year         = 2020,
  publisher    = {Zenodo},
  version      = {v0.4.2},
  doi          = {10.5281/zenodo.4158710},
  url          = {}

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